Note: Descriptions are shown in the official language in which they were submitted.
129309Ei
I~PROVE~ENTS RELATING TO E _ANUFACTURE OF TOBACCO
The invention the subject of the preseQt application
relates to the manufacture of tobacco smoke filter
elements.
The most widely established method o$ manufacture
of cigarette filter elements comprises the continuous
feeding of plasticiser treated cellulose acetate tow
and a web of wrapper paper to a garniture unit of a rod
making machine. A driven endless band extends through
the garniture unit and serves to convey the tow and
wrapper paper web through the unit, wherein the wrapper
paper is wrapped about the tow and lap seamed, there
thereby being continuously produced a rod of circular
cross-section. Downstream of the garniture unit the
rod is cut into lengths a multiple, commonly six, of a
unit element. Subsequent cutting of the rod lengths
during the making of filter tipped cigarettes provides
discrete filter elements. A similar method is used,
although to a lesser extent, for the manufacture of
paper filter elements, a web of crimped filter paper
rather than cellulose acetate tow being fed to the
garniture unit.
There have also been proposed methods of making
filter rod ~y the extrusion of foamed thermoplastics
materials. Such proposals have been disclosed in
United Kingdom Patent Specification No. 451,683
(Sharman), United Kingdom Patent Specifications Nos.
~,
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1,271,274; 1,341,400;1,442,631,1,456,908 and
1,482,216 (Monsanto Chemicals Limited or ~onsanto
Limited) and in United States Pa~ent Specification No.
4,180,536 (Celanese Corporation).
~ention is made iD United Kingdom Patent Specific-
ation No. 694,436 (Mayer-Neville) of a cigarette filter
element formed by rolling into cylindrical form a strip
of porous latex foam. Similar filter elements are
disclosed in United Kingdom Patent SpeGification No.
799,781 (Cogepa).
United Kingdom Patent Specifications Nos. 1,122,661
and 1,279,803 (Monsanto Chemicals Limited) relate to
cigarette filter elements made from an extruded, foamed
thermoplastic material which has been drawn, to impart
unidirectional orientation to the material, and then
worked in order to break down the foam structure and to
produce a three dimensional structure of interconnected
fibre elements.
United Kingdom Patent Specification No. 993,602
(Du Pont) teaches a method of making cigarette filter
rod wherein a polyoxymethylene is extruded as a foamed
structure ribbon, the ribbon is shredded under the
action of a wire brush and tbe shreds are wrapped in a
paper web. United Kingdom Patent Specification No.
1,183,498, in the name of the present applicants,
teaches the comminution of synthetic foam materials,
as for example in a hammer mill, and the wrapping of
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the resultant particulate material in paper to provide
filter rod. A class of foam materials disclosed in
United Kingdom Patent ~pecification No. 1,205,766
(National Patent Development Corporation) is said
6 to provide a suitable tobacco smoke filter medium,
especially when the materials are in particulate form.
According to United Kingdom Patent Specification No.
1,194,492 (Strickman Foundation), a tobacco smoke
filtration material is provided by granulating a rigid
polyurethane foam.
It is proposed in United States Patent Specific-
ation No. 3,800,808 (Brown & Williamson Tobacco
Corporation) to make cigarette filter material by
encasing a starch with a cellulose ester, cellulose
acetate for e~ample, swelling the starch and then
removing the starch by enzymation and/or chemical
hydrolysis or by solubilising the starch. The resultant
foamed product is cut into shreds, which shreds are
used as filter material for filter rod.
Although numerous proposals have been made in the
patents literature for the use of foamed materials in
or as cigarette filters, these proposals have failed to
find practical application in the tobacco industry.
It is an object of the present invention to provide
a method of making commercially acceptable filter rod,
which method is practical and simple. It is another
object of the present invention to provide a method in
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which readily available and inexpensive materials can
be used to make commercially acceptable filter rod.
The subject invention provides a method of making
filtration material, wherein a foamed extrudate is
S produced by providin~ to an extruder a particulate
plastics material, a polysaccharide expansion agent
and water, the conditions of heat and pressure in said
extruder being such that upon emergence of the extrudate
from the extruder die the extrudate assumes a cross-
section greater than that of the exit orifice of saidextruder die.
The plastics material is suitably polypropylene,
cellulose acetate, or polyethylene. The plastics
material may also be a polyester, viscose or nylon.
If cellulose acetate is used, it may be derived from
waste cigarette filters. Two or more plastics materials
may be fed together to the extruder.
The polysaccharide used as an expansion agent may
be a natural starch such, for example, as corn starch,
or a modified starch. As an alternative the
polysaccharide may be a cellulose, which term includes
food grade cellulose, or a modified cellulose, methyl
cellulose for example.
Other materials, chalk for example, may be fed to
the extruder with the plastics material and the starch.
The materials fed to the extruder may include a
binder, the inclusion level of which typically does not
1293098
exceed 5%. Cellulosic binders, hydroxypropyl cellulose,
carboxymethyl cellulose or sodium carboxymethyl cellu~ose
for example, are especially useful. Alternatively, or
in addition, a natural, or modified natural, binder
may be used, examples being pectin> or pectin salts,
and guar.
The m~terials fed to the extruder may include one
or more of a nucleating agent, such, for example, as
calcium carbonate or calcium acetate, a humectant such,
for e~ample, as glycerol, propylene glycol or sorbitol,
and a lubricant such, for example, as pharmaceutical
~ grade mineral oil.
The purpose of introducing water to the extruder
is to produce the foamed structure of the extrudate.
In the extruder the materials fed thereto are subjected
to conditions of heat, lOO C to 250-C for example, and
pressure such that immediately upon emergence from the
exit die of the extruder, the water, or at least a
portion thereof, flashes into steam, thereby creating
cells within the extrudate and a consequent swelling
of the extrudate. The water may be injected into the
extruder through ports in the extruder barrel and/or
be fed to the extruder via the feed hopper thereof.
Advantageously, the plastics material and the
polysaccharide, plus other materials if utilised, are
blended before being fed to the extruder.
The inclusion levels on a dry weight basis of the
I
12930'~8
materials fed to the extruder are 5% to 95% for the
plastics material and 95% to 5~5 for the polysaccharide.
The water may account, on a weight basis, for 1% to
20% of the materials plus water fed to the extruder.
The density of the extrudate may be in a range of
20 mgtcc to 500 mg/cc.
The extruder used in carrying out the inventive
process is suitably a twin-shaft cooker extruder.
Advantageously, the die of the extruder comprises
a slit-form exit orifice, whereby the e~trudate takes
the form of a flat web or ribbon. Alternatively, the
exit orifice of the die is such that the extrudate
upon first iSSUiDg from the die is of tubular or near-
tubular cross-section, the extrudate being then opened
to provide a flat web or ribbon. The die may according
to further alternatives be configured for the extrusion
of a strand or for the coextrusion of a plurality of
strands.
Advantageously, the extrudate when in web or ribbon
form is subjected to a draw down step, so effecting an
increase in the machine direction dimension of the
extrudate and a decrease in the thickness thereof.
When the extrudate takes the form, for example, of
a web or ribbon or a plurality of strands, it may be
fed continuously to the garniture of a filter making
machine, wherein it is gathered into rod form and
wrapped in a plugwrap, the process being similar to
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that commonly adopted in the making of paper filters
for cigarettes. Alternatively, a web, ribbon or strand(s)
may be shredded to provide pieces appro~imating iD
size to cut cigarette filler, the so provided particulate
material being then fed to a cigarette making machine,
wherein it is wrapped in plugwrap thus to provide
filter rod rather than cigarette rod. Advantageously,
before the extrudate passes to either of these rod
forming stages it is subjected to the cooling action of
cooling means.
The material fed to the filter or cigarette
making machine may be treated with a bonding agent.
Thus, for example, if the plastics material fed to the
extruder comprises cellulose acetate, a triacetin
bonding agent may be used. Again, for example, if
the plastics material comprises polypropylene, the
bonding agent may be a copolymer of ethylene and vinyl
acetate.
If the extrudate is of an open cellular interior
structure, the extrudate may take the form of a continuous
rod of the required filter rod circumference. In such
case the extrudate may be passed through sizing means,
tubular sizing means for example, in order to ensure a
consistent and accurate rod circumference. After
formation to size the rod is cut into, for example,
lengths six times unit filter element length.
Examples of the subject invention are as follows:
~293098
EXA~PLE I
A 50g:50~ dry blend of polypropylene granules and
Pfizer dietary fibre was fed to a Baker Perkins twin-
shaft cooker extruder at a feed rate of 9.5 Kg/hr. The
extruder was operated at a shaft speed of 110 r.p.m. and
with an outlet die temperature of 126'C. Water was fed
to the barrel of the extruder at a feed rate of one
litre per hour.
The resultant extrudate was a white, fluffy, soft
but self-sustaining rod of a density of 0.032 g/cc.
EXAMPLE II
A 50%:50% dry blend of polypropylene granules and
methyl cellulose granules manufactured by Celanese
Corporation under designation M450 was fed to the
extruder used in Example I at a feed rate of 16.0 ~g~hr.
The operating conditions were: shaft speed - 130 r.p.m.;
outlet die temperature - 140'C; and water feed rate -
two litres per hour.
The resultant extrudate was a white, bubbly, firm,
self-sustaining rod of a density of 0.053 g/cc.
The rods extruded in Examples I and II were suitable
for being shredded to provide pieces of cigarette
filler size for feeding to a cigarette making machine
for the manufacture of wrapped filter rod.
